A waveguide laser typically consists of two mirrors, concave or flat, defining an optical resonator cavity coupled together with a waveguide defining an optical path between the mirrors.
The waveguide is typically a channel ground into a ceramic block (e.g. aluminum oxide, Al2O3) with a lower electrode of aluminum or copper added to complete a cross-section of the waveguide. Alternatively, the waveguide can be ultrasonically drilled down through a piece of ceramic such as aluminum oxide (Al2O3) to create a continuous closed bore length with upper and lower electrodes parallel to the bore length. Typically, the positive arm of the oscillating electromagnetic field (e.g. Radio Frequency—RF) supply will be coupled into the upper electrode of the waveguide, and the ground plane of the RF supply will be coupled to the lower electrode. Resonance is added between and along the length of the upper electrode to distribute the RF voltage evenly along the length of the electrodes. Finally, the mirrors and waveguide structure are aligned and housed in a vacuum vessel (laser housing) that holds the gas to be excited.
Waveguide lasers suffer from the disadvantage that, for the lengths needed, the waveguides are difficult to fabricate with sufficient accuracy at a reasonable cost to obtain acceptable laser performance. It is very difficult to cost-effectively fabricate a typical waveguide structure that is roughly 30 to 40 cm long with a 1.5 to 3.0 mm bore. Bore cross-section inaccuracy leads to unacceptable laser transverse mode characteristics and reduced power output. Due to the size, current ceramic slabs used to manufacture waveguides are constructed by casting or extruded. Casting or extruding tolerances are high, requiring expensive machining (grinding) after the piece is formed to acquire the desired accuracy.
Additionally, a waveguide laser balances it's loss in inherent internal RF circuit, and heat removal efficiency. Ideally, to minimize the RF losses the capacitance between the top and bottom electrodes (RF+ and RF− or ground) needs to be high, which translates into using as little ceramic as possible between the top and bottom electrodes. With Al2O3, thermal efficiency requirements dictate the use of a large ceramic area, which creates either a higher loss RF circuit, and/or high manufacturing costs. Ideally materials with good thermal properties such as BeO and AlN are desirable ceramics to use, but are prohibitively expensive with related art waveguide designs.
Additionally, the resonator cavities of waveguide lasers suffer energy losses from misalignment of the containment mirrors and low reflectivity properties of the containment. For example, the use of planar mirrors at either end of the resonator cavity, unless perfectly aligned, enable only a limited number of reflections.
Since the bore cross-sections, in the related art, are the result of grinding or ultrasonic drilling, most bores are either rectangular or circular. This results in bores that are optimized for the manufacturing process rather than the optical properties of the device. For example, the use of curved containment mirrors results in variable beam radius throughout the resonator cavity, thus the waveguide channels of related art fail to allow the optimization of the waveguide with respect to variable beam radius in the resonator channel.
In related art, the electrode positioning, and subsequent resonance electric field generation, is partly a function of the electrode spacing, and is often determined by the size of the waveguide structure (i.e. the distance between electrodes). Various spacing between electrodes results in varying power levels and the related art fails to fully optimize the electrode spacing and optics, and instead conventional methods focus on ease of manufacture.
Additional problems exist in conventional gaseous lasers, for example, laser startup. Traditional CO2 lasers are pressurized at 70–80 torr and have difficultly starting without some manipulation of the RF system.
A related art system is described in Laakmann (U.S. Pat. No. 4,169,251). Laakmann is directed to a conventional waveguide laser that suffers from many of the same problems as other conventional systems (e.g., expensive long ceramic pieces that must be formed via casting, conventional startup characteristics . . . ).